1. Field of the Invention
The present invention relates generally to rotational sensors and particularly to a gyroscope incorporating an ionization contact potential difference detector.
2. Description of Related Art
It has long been desired to eliminate sources of error from gyroscopes. Friction is a main contributing factor in the production of such errors. First order effects such as excessive drift, and bearing friction and gimble bearing friction produced precession are common with gyroscopes incorporating mechanical methods of restraint and support for the proof masses and gyroroters. Second order effects such as tumbling, gimble lock and coning errors are similarly undesirable.
Ring laser gyroscopes overcome many of the shortcomings of mechanical gyroscopes. A ring laser gyroscope is an instrument which employs the Sagnac effect to measure rotation rate. A ring laser gyroscope is a device comprising an arrangement of mirrors for directing light beams around a closed path through a gain region comprising a lasing gas and an arrangement of electrodes for creating an electrical discharge in the gas and a means for measuring the frequency difference of light beams thereby generated that are propagated around the closed path in opposite directions. The frequency difference of the light beams is a measure of the rotational rate of the ring laser gyroscope in the plane of the light beams. Yet, the expense of the ring laser gyroscope is one of its major drawbacks.
Another attempt to limit conventional gyroscopic errors is taught in U.S. Pat. No. 3,965,753 to Browning, Jr. This patent is directed to a sensing device, including an electrode assembly formed by three pairs of electrodes that creates a three axis electrical field surrounding a charged particle confined in a sealed space consisting either of a vacuum or one filled with a selected gas. The field is energizable to support the particle centerably in a state of stable equilibrium. A detector mounted exteriorly with respect to the electrode assembly is responsive to displacement of the particle from the central position. Such a displacement can be, for example, acceleration due to gravity or other motion, and a restoring force in operable association with the detectors. The electrical field is triggered by the displacement to return the particle to the central position. Yet, the Browning, Jr. sensing device is plagued with electro-magnetic instability, a high cost of manufacture and limited sensitivity.
In view of the above, there exits a need to provide a sensing device that limits the use of moving parts, or eliminates moving parts altogether. Further, there is a need for a sensing device that is more accurate than the conventional mechanical gyroscope, more economic than a ring laser gyroscope, and more stable and more sensitive than prior art designs. Another disadvantage in the gyroscopic art is the limited range of possible miniaturization of conventional gyroscopes. Thus, it would be further beneficial to provide a sensing device that is capable of a range of sizes, including use in nanotechnology applications.
U.S. patent application Ser. No. 09/553,780 (the xe2x80x9c""780 Applicationxe2x80x9d) discloses a contact potential difference ionization probe that provides both a nondestructive testing method of condensed matter surfaces, and a sensing device for the measurement of the work function of the surface of a conducting or semiconducting sample. This ""780 Application is fully incorporated herein by reference. The contact potential difference ionization detector has no moving parts, yet is sensitive enough so as to be capable of sensing gas currents due to the separation of ionized gases by the differences in chemical potential between two different metals. General principals of the ionization probe of the ""780 Application are utilized to provide the superior gyroscopic device of the present application.
Briefly described, in a preferred form, the present invention is an extremely sensitive solid state gyroscope that is of such versatile construction that it can be utilized in a number of different applications, including the area of nanotechnology. The present solid state gyroscope is constructed in part on the principle of the ionization contact potential difference (Kelvin) probe. The gyroscope in the preferred embodiment comprises plates, a measurement circuit, an ionization source and a housing. The plates are two different metals inside the housing arranged so as to form the plates of a capacitor, and the plates are electrically connected by the measurement circuit. When the plates are electrically connected, the contact potential difference in the space between them creates an electric field between the plates. An ionization source is provided to ionize the gas located between the two plates. The electrical field created by the contact potential difference in the space between the plates separates the ions. As the ions strike the plates, an electrical current is generated in the measurement circuit.
The two plates of the gyroscope are enclosed in a sealed housing that is filled with a gas made up of heavy molecules that are polarizable. With the two plates stationary, the ionized gas strikes the plates and produces a current in the measurement circuit. If the plates are moved relative to the gas, the inertia of the molecules between the plates relative to the motion of the plates causes the electrical current to change, and the change in electrical current is related to the motion of the plates. The contact potential difference measurement circuit is capable of measuring the change in the current by a difference in the signal from the two plates. The measurement circuit of the present invention is capable of sensing the small amount of electrical current caused by motion of the ions moving between the plates. Due to a difference in the ionization of the atoms in the gap between the plates of the two probes and due to the difference in the adsorption layers on the plates of the two probes.
The housing can be filled with one or more gases. Mixtures of more than one gas is believed to provide a better signal than a pure substance, although a pure substance can also be used. Molecules with large dipole moments and heavy centers of inertia are believed to provide a more accurate gyroscope. With a mixture of gases, it is likely possible to take advantage of molecular collisions and interactions to gain a stronger polarizing effect.
The gyroscope can include a pair of plates for each degree of freedom that is to be monitored. Thus, a gyroscope comprising three sets of plates in addition to a ground plate, each at 90 degrees to each other, would be capable of monitoring three dimensional motion. The present gyroscope advantageously also has no moving parts and can easily be miniaturized.
Thus, an object of the invention is to provide an improved gyroscope. Another object of the present invention is to provide an improved gyroscope that is extremely sensitive to relative motion. These and other objects, features, and advantages of the present invention will be more apparent upon reading the following specification in conjunction with the accompanying drawings.